The present invention relates to a process for efficiently absorbing and eliminating impurities in electric insulating liquids by means of a combination of high electric field action and ion-radical absorbent action. These impurities consist primarily of low molecular weight materials ordinarily present in low concentrations in the electric insulating liquid.
At present, oily liquids, such as vegetable or mineral oils are used as insulating liquids and these materials are relatively pure electric insulating liquids per se. However, the life of such insulating oils depends upon the degree of refinement of the polar compounds or unsaturated compounds which are present in the oils, when a low degree of refining of such oils is carried out. Such polar and/or unsaturated compounds serve to deteriorate the electric insulating capacities of the liquid by, e.g., making them more conductive and thus such polar and unsaturated compounds are undesirable.
In addition to being deteriorated by the undesirable contaminants described above, the conventionally used oily insulating liquids are deteriorated as a result of polymerization caused by the existing oxygen or hydrogen in the liquids or by condensation due to the existence of hydrogen generated from a CORONA discharge when used as an electric insulating liquid. To counteract the above, the insulating oils should be refined as highly as possible before pouring into an electrical device so as to eliminate electrically conductive impurities of low molecular weight at low concentrations as discussed above, which contaminants apparently represent the chief cause of deterioration of these lquids.